Younan Xia

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Nanostructured Materials
Younan Xia Department of Chemistry University of
Washintgon Seattle, Washington 98195 E-mail
xia_at_chem.washington.edu
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What Are Nanostructures?
These days, you cant swing a dead cat without
hitting something with the word nano on it.
CEN News, 2003, April 28, p. 27
Nano
Molecular
Meso
H-atom benzene buckyball
soap molecules micelles dendrimers Q-dots hemoglo
bin viruses carbon nanotubes gold nanoparticles
bacteria dusts blood cells hairs
colloidal particles
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Make It Smaller!
First Planar IC
First Transistor
(1958, Fairchild)
(1947, Bell Lab)
180 nm
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Moores Law Smaller Is Better!
Peercy, Nature 2000, 406, 1023
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Types of Nanostructured Materials
(1D)
(2D)
(0D)
Joannopoulos et al., Photonic Crystals, 1995
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Why Does Size Matter?
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Dependence of Surface Area on Size
no change in volume
r
r
R
r
r
volume 4pR3/3 N 4pr3/3
N R3/r3
new surface/old surface N 4pr2/4pR2 R/r
when R1 mm and r10 nm, the ratio is 100
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Pressure in A Droplet versus Size
Pout
Pin
Young-Laplace Eq.
r
DPPin - Pout 2g/r
for water, g7x10-2 N/m
when r1 mm, DP1.4x105 N/m2 or 1.4 atm
when r100 nm, DP1.4x106 N/m2 or 14 atm
when r10 nm, DP1.4x107 N/m2 or 140 atm
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Quantum Confinement Particle in A Box
DE (n22 - n12)h2/8mL2
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Q-Dots Tuning of Property by Size
Alivisatos, MRS Bulletin 1995, August, 23
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Q-Dots Same Substance, Different Colors
Alivisatos (UC Berkeley), Bawendi (MIT), Brus
(Columbia)
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Q-Dots Superior Fluorescent Markers
Superior Brightness Incredible Photostability Mult
i-Color Capability Single Excitation Source
http//www.qdots.com
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Quantized Conductance of Electrons
metal
A
L
G
Ohms Law
2e2/h 1/13 kW
G I/v s (A/L)
A
van Houten et al., Physics Today 1996, July, 22
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Metal-Insulator-Metal Junction
I
Al
Al
Al2O3
A
0
d
V
Q CV
C e0eA/d
8.85x10-12 Fm-1 8 (10x10 nm2/1 nm)
7.08x10-18 F
_at_100 mV, Q7.08x10-19 c, or 4 electrons
_at_25 mV, Q7.08x10-19 c, or 1 electron
_at_10 mV, Q7.08x10-19 c, or 0.4 electron
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Coulomb Blockade and Staircase
I
-e/2C
0
V
e/2C
Barner Ruggerio, Phys. Rev. Lett. 1987, 59, 807
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Different Approaches to Nanostructures
Top-Down
Bottom-Up
Ozin, Adv. Mater. 1992, 4, 612
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Contact Mode Photolithography
photon
chrome
photoresist
quartz
substrate
substrate
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Non-Contact Mode Projection
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Resolving Power (d) of An Optical Lens
Limit placed by diffraction
d 0.61 l / NA
NA the numerical aperture of a lens, and NA n
sina n the refractive index of the medium
above the sample a the acceptance angle
lens
a
in air, n1, dmax 0.61 l for visible light,
300 nm
sample
when a45 degrees, d l
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Electron-Beam Lithography
Resolution 1-3 nm
lh/(2meV)1/2
100 kV, l4 pm
FEI Siron XL 30 UW NanoTech Center
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Soft Lithography An Alternative Strategy
Whitesides Love, Sci. Am. 2001, 285(3), 38 Xia
Whitesides, Angew. Chem. 1998, 37, 551
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Bottom-Up Approach Chemical Synthesis
UW Bagley Hall, Room 16
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Q-Dots Made by Arrested Precipitation
Whitesides Love, Sci. Am. 2001, 283(3),
38 Alivisatos, MRS Bulletin 1995, August,
23 Bawendi et al., J. Am. Chem. Soc. 1993, 115,
8706
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Anisotropic Growth Induced by Structure

• Intrinsic Optical Chirality
• Highest Photoconductivity
• (s 8x104 S/cm for t-Se)
• Piezoelectric Nonlinear
• Optical (NLO) Properties
• Thermoelectric Properties
• Useful Catalytic Properties
• (Halogenation, Oxidation)
• Reactivities to Form Other
• Functional Materials such
• as CdSe, CuSe, and Ag2Se

Trigonal Selenium (t-Se)
Se Spiral Chain
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Synthesis of Uniform Nanowires of t-Se
100 oC
100 oC
a-Se
R.T.
a-Se
DG
t-Se
(t-Se)
a-Se
t-Se
Gates, Yin Xia, J. Am. Chem. Soc. 2000, 122,
12582
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Various Stages of Nanowire Growth
Gates, Mayers, Cattle Xia, Adv. Func. Mater.
2002, 12, 219
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Formation of Uniform Silver Nanowires
AgNO3 HO(CH2)2OH
PtCl2
XRD
(PVP)
PVPAg11
160-180 oC
Sun, Gates, Mayers Xia, Nano Lett. 2002, 2, 165
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One-Dimensional Photonic Crystals
Plane-Wave-Expansion-Method (PWEM)
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Photonic Band Structures of 1-D Systems
Band Gap
w(c/e1/2)k
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Opals and Self-Assembly of Colloids
Sanders, Nature 1964, 204, 1151
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Crystallization of Spherical Colloids
Lu, Yin, Gates Xia, Langmuir 2001, 17, 6344
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Photonic Band Structure and Spectra
Photonic Band Structure
Trans./Refl. Spectra
Xia, Gates Li, Adv. Mater. 2001, 13, 415
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Inverse Opal and Photonic Properties
Remove Template
(n2/n1 3.0)
Xia, Gates, Yin Lu, Adv. Mater. 2000, 12, 693
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Diffusion Coefficient (D) versus Size
Random-Walk Eq.
Stokes-Einstein Eq.
ltd2gt1/2 (2Dt)1/2
D kBT/6phr

• for cells, r is around 10 mm
• for bacteria, r is around 1 mm
• for viruses, r is around 10 nm (0.01 mm)